Holders for gem stones



p 16, 1969 A.1 ElBowlTz 3,466,812

' HOLDERS FOR GEM STONES Filed Jan. 23. 1967 United States Patent 3,466,812 HOLDERS FOR GEM STONES Alec Leibowitz, London, England, assignor to Spectrum Diamonds (Proprietary) Limited, Johannesburg, Transvaal, Republic of South Africa, an African company Filed Jan. 23, 1967, Ser. No. 611,055 Claims priority, application Republic of South Africa, Feb. 2, 1966, 66/624 Int. Cl. B24b 9/16 U.S. Cl. 51--229 7 Clanns ABSTRACT OF THE DISCLOSURE A holder for supporting a gem stone on a polishing wheel comprising an elongated metal body provided with a compartment at its front end for retaining a gem carrying press-pot, an outer polishing guide ring, and an insulating sleeve in the body for electrically insulating the outer ring from a press-pot held in the compartment.

This invention relates to a holder for supporting a gem stone during polishing.

It is conventional to polish a gem stone for example a diamond, by gripping it in a press-pot which in turn is gripped by a holder, with the holder being located in a dop. The dop in turn is attached to an arm which is used to locate the gem over aifiolishing wheel, and such arm is referred to in the art as a tang.

It is known to provide press-pots which are made of suitable metal shaped in the form of an elongated pear. At the blunt or leading end 0% the pear, a cavity is defined in which the gem stone is to be located and the pear is split axially from the blunt end to a point towards the sharp end so that a series of fingers are provided. These fingers expand radially outwardly to permit the gem to be located in the pot or cavity and on radially inward movement of the fingers, the gem is gripped sufliciently tightly for polishing to be carried out on an underlying wheel. Radially inward movement of the fingers is accomplished by pushing the press-pot axially into a bore in the leading end of the polishing holder.

In operation, the holder and the press-pot are normally inclined to the vertical and polishing takes place in a plane which will ultimately cause contact to be established between the leading tip of the press-pot and the wheel surface.

The invention is directed to a holder for supporting a gem stone during polishing, the holder comprising a compartment at its forward end adapted to hold a gem stone carrying pot inserted therein, an outer ring of electrically conducting material whose forward end can be used as a guide for terminating polishing when it contacts a polishing surface, and means for insulating the outer ring from a press pot inserted into the compartment.

The invention also provides a holder, as set out in the preceding paragraph, including means to adjust its effective length. For instance, a cylindrical nut may be located on a threaded shank provided at the rear end of the holder and by screwing the nut axially outwardly the efiective length of the holder is increased. Likewise, when the nut is turned up on the threaded shank, the effective length is shortened.

In order to illustrate the invention an example is described hereunder with reference to the accompanying drawing showing a cross-section through a holder and a press-pot for insertion therein.

The holder is a cylindrical piece of suitable metal which is bored centrally to provide a bore 1 through which a tool may be passed to eject a press-pot. A press-pot compartment 2 is provided in the leading end of the holder and the bore 1 communicates with the compartment via a bore 9. At the rear or trailing end of the holder, a threaded shank 3 of reduced diameter is located and a nut 4 is fitted onto the shank. The nut and the holder body are of uniform diameter and the nut and rear portion of the body are adapted frictionally to engage in a bore in a dop. (The shank and threaded nut could alternatively be replaced by a suitable headed screw and threaded hole in the end of the holder.)

By means of the nut the effective length of the holder may be varied to adjust for dilferent projections of gem stones from the press-pot.

The compartment in the holder for the press-pot accommodates a metallic sleeve insert 5 for gripping the presspot and a nylon insulating sleeve 7 is located between the insert and outer walls 6 of the holder. A metal ring 8 is frictionally fited over the cylindrical body of the holder and the metal ring is capable of axial movement into any desired position. It will be seen that when a press-pot is inserted into its compartment, the press-pot will be electrically insulated from the remainder of the holder by the insulating sleeve 7. However, it is possible to establish electrical connection between the pot and the holder through the bores 1 and 9.

The form of press-pot employed is conventional and includes a metal pear-shaped body 10 which is adapted to be inserted in the compartment 2 with its blunt end projecting therefrom. In the blunt end a cavity (not shown) is provided for the accommodation of portion of a gem stone and the sides of the press-pot are split axially to define a series of fingers a, b and c. These fingers expand radially to permit a gem to be fitted into the pot and contract to grip the gem. Radial contraction is etfected when the press-pot is pushed into the compartment in the holder.

The leading end of the press-pot tapers outwardly, and a slope or bevel is also provided on leading edge 11 of the ring 8 surrounding the holder body.

When a stone is to be polished, the press-pot is opened to permit the back of the stone to be inserted in the cavity in the leading end of the press-pot. The press-pot is then pushed into the compartment 2 so that radial contraction of the fingers takes place with the stone firmly gripped therebetween. The ring is then advanced to ensure that during polishing, when the required depth of polish is obtained, the leading edge 11 of the ring contacts the polishing surface. An electrical circuit can then be completed between the polishing plate, ring and holder, and the operation terminated. If, during polishing, the pot contacts the polishing plate, no electrical circuit will be completed through the holder since the pot is insulated. However, if it is necessary to establish such a circuit (for example in carrying out a method according to U.S. patent application No. 690,916, filed Dec. 15, 1967), then electrical contact can be made with the pot through bores 1 and 9.

When the stone has been polished, it is removed from the press-pot for a further stone to be inserted therein. Any differences in the extent to which the stone projects from the press-pot is taken into account by adjusting the nut on the threaded shank at the rear end of the holder.

Many more examples of the invention exist with each differing from the other in matters of detail only. The essence of the invention is the provision of the ring or other suitable device insulated from the pot for use with a guide to terminate polishing and thereby provide a depth control in regard to polishing. The ring need not be axially slidable, but could be fixed in a suitable position, or could comprise or form part of the walls 6.

I claim:

1. A holder for supporting a gem stone during polishing, said holder comprising a body of electrically conducting material, wall means defining a cavity at a forward end of said body for gripping an elongate gem carrying press-pot, a ring of electrically conducting material mounted on an outer surface of said body, said ring having a circumferentially continuous front edge useful as a guide for terminating the polishing of each of a series of facets around said gem, and insulating means Within said body between said wall means and said outer surface for electrically insulating said presspot from said ring.

2. A holder as claimed in claim 1 in which said cavity has a walling of conducting material and said insulating means is a sleeve surrounding said walling inwardly of said ring.

3. A holder as claimed in claim 1 in which said ring is axially adjustable for position along the said holder body.

4. A holder as claimed in claim 1 including means for adjusting the efiective length of said holder.

5. A holder. as claimed in claim 4 in which said adjusting means comprises screw adjustment means at the rear end of said holder.

6. A holder as claimed in claim 1 having a longitudinal bore formed therethrough leading into said cavity. Y

7. A holder as claimed in claim 1 having a gem-carrying press-pot inserted into said cavity.

References Cited UNITED STATES PATENTS 2,270,420 l/ 1942 Dinhofer 51-229 2,393,939 l/ 1946 Spira 5l-229 2,513,139 6/1950 Burness 51-229 2,829,472 4/ 1958 Salzer 51-229 HAROLD D. WHITEHEAD, Primary Examiner Dedication 3,466,812.-Ale0 Leibo'un'te, London, England. HOLDERS FOR GEM STONES. Patent dated Se t. 16, 1969. Dedication filed Sept. 7, 1973, by the assignee, Spectrum iamonds (Proprietary) Limited. Hereby dedicates the entire remaining term of said patent to the Public.

[Ojficial Gazette December 25, 1.973.] 

